The modem trend is toward increased reliance on data communication. Data communication is an essential feature, for example, in commerce conducted over computer networks. Where sensitive information is communicated in personal or business transactions, privacy from interception of the information is an important aspect of the communication system relied upon for transmission of the information. This is especially true in wireless communication systems because the communication medium used by the wireless system, i.e., the atmosphere, is readily accessible by parties who are not intended recipients of the information. Wireless phone networks are another example of data communication systems in which privacy of communication is valued. Point-to-multipoint data systems, such as a cellular subscription television system, where a broadcast is provided to paid subscribers, are an additional example. Many other such systems which could benefit from increased privacy and from reduced power consumption will be apparent to artisans.
In particular, there is a growing concern over the privacy of wireless communication systems. Wireless systems place additional demands on the components of the systems. Personal communication devices, such as cell phones, and computers and personal organizers with wireless communication capability, form a primary component of the wireless systems. As the devices become smaller and lighter, there is a strong need to reduce power consumption as the available battery power life is reduced when smaller batteries are used. In addition, reduced power consumption is generally desirable even when battery life is maintained or increased because reduced power consumption leads to a longer period of device operation without replacement or recharging of the battery used for power. Particular applications which benefit greatly from reduced power consumption are military applications since many devices in military communication systems depend upon portable power sources. Military applications also have a particular need for privacy from both detection of communications and decoding of information transmitted during communications. Law enforcement applications also particularly benefit from such privacy.
Chaotic dynamical systems have been proposed to address the problem of communication privacy. Chaotic signals exhibit a broad continuous spectrum and have been studied in connection with spread spectrum applications. The irregular nature of a chaotic signal makes it difficult to intercept and decode. In many instances a chaotic signal will be indistinguishable from noise and interference to receivers not having knowledge of the chaotic signal used for transmission. An important development in the use of chaotic systems was the ability to synchronize coupled chaotic systems to produce identical chaotic oscillations. See, Synchronization in Chaotic Systems, L. M. Pecora and T. L. Carroll, Phys. Rev. Lett., 64:821-824, 1990, A Simple Way to Synchronize Chaotic Systems with Applications to Secure Communication Systems, Int'l J. of Bifurcation and Chaos, 3(6):1619-1627, 1993, Synchronized Chaos in Electronic Circuits, N. F. Rul'kov and A. R. Volkovskii, from Chaos in Communications, edited by Louis M. Pecora, pp. 132-140, SPIE--The International Society for Optical Engineering, Bellingham, Wash., 98227-0010, 1993, all three of which are incorporated by reference herein.
Various chaos based communication systems have been proposed. A difficulty with chaos based communications is their extreme sensitivity to phase distortions due to their nonlinear nature. Many of the prior art systems are therefore very sensitive to distortions, filtering and noise. The negative effect of filtering limits the ability of these types of systems to rely on filtering to improve performance, and makes them more susceptible to distortions that naturally occur in communication channels.
Accordingly, there is a need for an improved communication system. In particular, there is a need for an improved chaos based communication system which has reduced sensitivity to distortions and noise. It is an object of the invention to provide such an improved chaos based communication system and method.
It is a further object of the invention to provide such an improved communication system with a low power consumption for transmission and reception of data.